The proposed research deals with the influences of the technology of contraception upon the decline in marital fertility observed among significant segments of the American population during the era 1850-1920. It is designed to provide what will be the first quantitative historical account of the early adoption and subsequent diffusion of contraceptive practices among middle-class families in Victorian America, and to test existing and new hypotheses about the economic, social, and personal characteristics of those who engaged successfully in family limitation. The research strategy integrates four quite novel lines of investigation, each of which has yielded promising preliminary results described in the proposal. These lines of investigation include: (1) Significant formal extension of economic and socio-economic models of fertility regulation, which goes beyond existing theories by taking explicit account of the biological nexus between sexual behavior and fertility. The latter proves particularly important in studying populations that do not have access to modern, highly reliable contraceptive technologies. (2) Construction of micro-demographic models whose details (in regard to the interaction of behavioral and biological determinants of fertility) make possible realistic computer simulations of alternative life-cycle strategies of family limitation, including adaptive as well as non-adaptive patterns individual behavior. (3) Exploitation of two newly available bodies of quantitative data. One comprises a small unpublished set of richly detailed responses by married middle-class women who were systematically interviewed on their sexual and reproductive experiences by a woman physician during the period 1892-1920. The other consists of large-scale stratified random cluster sample of individual fertility histories, which we propose to draw from the manuscript schedules of the U.S. Census of 1900. (4) Development of a statistical methodology involving classification analysis, which extends existing demographic techniques and makes it possible to arrive at probabilistic inferences concerning the distribution of family limitation practices in a given population from a representative sample of individual birth interval histories.